<template>
    <ul class="list">
        <li class="item"
            v-for="item of letters"
            :key="item"
            :ref="item"
            @touchstart.prevent="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd"
            @click="handleLetterClick"
        >
            {{item}}
        </li>
    </ul>         
</template>
<script>
export default {
    name: 'CityAlphabet',
    data() {
        return {
            touchStatus: false,
            startY: 0,
            timer: null
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop;
    },
    computed: {
        letters() {
            const letters = [];
            for(let i in this.cities) {
                letters.push(i);
            }
            return letters;
        }
    },
    props: {
        cities: Object
    },
    methods: {
        handleLetterClick (e) {
            this.$emit('change', e.target.innerText);
        },
        handleTouchStart () {
            this.touchStatus = true;
        },
        handleTouchMove (e) {
            if (this.touchStatus) {
                if (this.timer) {
                    clearTimeout(this.timer);
                }
                this.timer = setTimeout(() => {
                    const touchY = e.touches[0].clientY;
                    const index = Math.floor((touchY - this.startY) / 20);
                    if (index >= 0 && this.letters.length) {
                        this.$emit('change', this.letters[index]);
                    }
                }, 16);
            }
        },
        handleTouchEnd () {
            this.touchStatus = false;
        }
    }
}
</script>
<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.list 
    display: flex
    flex-direction: column 
    justify-content: center 
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
        line-height: .44rem
        text-align: center
        font-size: .2rem
        color: $bgcolor
</style>


